His father Quintus Marcius Rex, the praetor in 144 BC, built the Aqua Marcia aqueduct, the longest aqueduct of ancient Rome.
The aqueduct was known for its water purity and its cold temperature.
Marcius carried on a war against the Stoeni, a Ligurian people at the foot of the Alps, and obtained a triumph in the following year on account of his victories over them.
During his consulship in 118 BC, Marcius lost his only son, a youth of great promise, but had such mastery over his feelings as to meet the senate on the day of his son's burial, and perform his regular official duties.
Through his son, possibly named Quintus Marcius Rex, he had a grandson also named Quintus Marcius Rex, who was the consul in 68 BC.